1. Field of the Invention
The invention in general relates to disposable dry test strips for testing bodily fluids, and more particularly to a method and apparatus for manufacturing such test strips.
2. Statement of the Problem
The level of certain analytes in blood and other body fluids is often used to diagnose disease, determine disease risk factors, monitor the course of a therapy, or determine the presence of illicit drugs. In recent years, analytes carried in blood have been evaluated to determine various cholesterol and triglyceride levels as a significant indicator of risk of coronary heart disease. Physicians commonly order what is referred to in the art as a “full lipid panel” for patients to determine the concentration of total cholesterol, high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), and triglycerides.
The blood analysis necessary to determine bodily fluid analytes, such as cholesterols, may be performed in a clinical setting in a laboratory or on site using dry test strips. In the laboratory, the blood is centrifuged to separate the red blood cells from the plasma, and carefully controlled chemical tests in test tubes are performed to determine the concentration of analytes. Dry test strips utilize several membrane layers to separate red blood cells from blood plasma, react the plasma with a particular reagent or reagents, and obtain a signal indicative of the concentration of a particular analyte. See, for example, U.S. Pat. No. 4,774,192 issued Sep. 27, 1988 to Terminiello et al.; U.S. Pat. No. 4,477,575 issued Oct. 16, 1984 to Peter Vogel et al.; U.S. Pat. No. 5,135,716 issued Aug. 4, 1992 to Tatin B. Thakore; U.S. Pat. No. 5,597,532 issued Jan. 28, 1997 to James Connolly; U.S. Pat. No. 6,171,849 issued Jan. 9, 2001 to Walter Rittersdorf et al.; U.S. Pat. No. 6,759,190 issued Jul. 6, 2004 to Jinn-Nan Lin et al.; United States Patent Application Publication No. US2004/0126830 published Jul. 1, 2004 on an invention of Bruce Shull et al.; and United States Patent Application Publication No. US2005/0003523 published Jan. 6, 2005 on an invention of Sunil Anaokar et al.
FIG. 1 illustrates the conventional manufacturing process of a dry test strip. Test holder assembly 100 includes a plurality of test strip holders 101, 102, 103, 104, and 105. FIG. 1 also shows a roll 110 of test membrane strip 112, which has been partially unrolled across holder assembly 100. As is known in the art, the test membrane strip 112 is a multilayered structure, the layers of which have been previously impregnated with the chemicals required for the test. An element of the test membrane strip 112 is cut away to show the sensor port 136 of holder 104. The holders 103-105 are joined together along score lines, such as 108. A typical holder 104 includes a main body portion 120 and a cover portion 122. The cover portion of each holder, such as 104, is folded at the line 129 between cutouts 127 and 128 so that holes, such as 124, snap onto posts, such as 126, to lock the membrane 112 in place with sample port 145 located directly above sensor port 136. The individual holders 101, 102, etc., then are cut apart at score lines, such as 108. The cutting process also cuts the test strip 112 into rectangles, such as 117, between the dotted lines at each side of holder 102, each rectangle of test strip being held between the cover, such as 122, and body, such as 120, of the corresponding test holder. The completed holder, such as 102, with its corresponding test strip rectangle, such as 117, held in place makes a completed individual dry test assembly 129. While only five holders are shown in the manufacturing assembly 100 of FIG. 1, generally there are many more holders in a manufacturing assembly, which is illustrated by the dashed lines 106 and 107 in FIG. 1
The above-described manufacturing process permits a semi-automated manufacturing process, in that a roll 110 of membrane can be applied across a large number of holders in a single process, and the process of separating the holders 101, 102, etc., also cuts the membrane into separate test elements while the individual test elements, such as 117, are trapped between the cover, such as 142, and main body, such as 140. However, as will be shown in detail below, this manufacturing process also contributes significantly to the inaccuracy of the prior art test strip.
Dry test strips have the advantage that relatively unskilled people at the site where the test is ordered or needed can perform them in a few minutes. However, since the chemistry required to perform the test is in place in the strip, it cannot easily be varied depending on the particular sample to be tested, and the user may not always apply the same amount of bodily fluid via the sample port 145. This results in an inherent inaccuracy of the conventional dry test strip measurement as compared to a clinical process performed in the laboratory, where the bodily fluid and chemicals can be more carefully measured. Further, since the strips are mass produced, they are subject to manufacturing variations that are determined by the manufacturing process. Thus, dry test strips, while very convenient, are more inaccurate than clinical analyses, and their usefulness is limited to situations in which high accuracy is not required. If the inaccuracies due to manufacturing variations could be reduced significantly, a much more useful test strip would result.